Posterous created a how-to video that demonstrates the steps necessary to create your own group blog using Posterous. The video includes how to make your Posterous group site private.
WordSift is another visualisation tool that was created primarily for teachers. It works just like Wordle but just a bit better. All you need do is paste in the text and then sit back. The sifted words then show up in orange or green and the fun really begins. This tool would be lots of fun on an IWB as well as on your own computer. Don't miss checking out the About section for more thoughts on using it. - comment by John Pearce
These math games look great. The only problem I can see is that once a student has played once, they must close out to play again. New questions do come up if they choose to play again though.